Electric_Light

I just noticed that a 24kcool/75kheat unit from 1990 has a factory charge of 40 oz where as an adjacent 2007 unit with 24k/60k capacity has a factory charge of 70oz. They're both running R-22.

They're both Ruud units. Why does the newer design use almost twice as much refrigerant? Is it a reserve to allow for more leak before needing service??

NickTech

the 1990 is probably a 9 or 10 seer. the 2007 must be a minimum of 13 seer as of '06. the higher the efficiency the larger the coils need to be. with the larger coils comes more space to fill up with refrigerant.
BTW, units are charged with the exact amount of refrig needed to operate, not "with a lil extra in case of leaks"

Electric_Light

Ah, that makes sense. The 2007 unit is MUCH bigger physically too.

I'm guessing package units are much less prone to leaks and perform more consistently since you don't have techs doing the pipe brazing and there is no technician discretion in using the gauges and measuring temperatures to charge. I read somewhere that overcharge is quite a common problem with a split system.

So, am I correct to think that the best way to have a package unit charge is to have it evacuated, then filled to factory spec by weight just like on automotive system?

flashheatingand

Overcharging does happen. But most outfits check out the charge before leaving the job. If they charged the system via super-heat, sub cool, they should be alright. You can weigh in the charge as explained, but bottom line is you want a certain level of SH, and the compressor should be drawing X amount of Amps.

Actually, it's better to not mess with the charge unless there are problems with the cooling system.

Electric_Light

Well, the system is 20 years old, so I'm pretty sure it's lost some charge, so I'm tempted to have it evacuated then, recharged by weight. It's probably got some acid built up too.

NickTech

not so fast. i've worked on old r12 chrysler airtemp a/c systems frm the 50's w/o leaks. and split systems over 20 yrs old with the original charge. ya cant assume anything, proper test methods with tell you exactly what the system is doing and what the charge is. and acid is only formed when moisture enters the system and makes hydrochloric and hydrofloric acid. an acid test kit will prove so.

flashheatingand

You risk awaking a sleeping giant. If the system has been fine for 20 years, don't mess with the charge. Want to get the most life out of the appliance? Just keep the coils clean, get the dust off the motors,and make sure the condensate drains alright.